The present invention relates to an extension tube which can be connected between the lens mount of a camera body and an interchangeable lens assembly, so as to extend the lens assembly along its optical axis forwardly of the camera body.
It is known to provide an extension tube or barrel between a camera body and an interchangeable lens assembly, thereby extending the lens assembly forwardly of the camera body to make it possible to carry out close-up or copy photography. A wide variety of different types of extension tubes are available, corresponding to the various exposure adjustment arrangements provided between the diaphragm of the lens assembly and the diaphragm control mechanism in the camera body. The present invention relates to an extension tube or barrel adapted to be connected between an interchangeable lens assembly which includes an aperture indicating member and a diaphragm actuating member associated with a diaphragm presetting mechanism and a diaphragm device in the lens assembly, and a camera body which includes corresponding indicating and actuating members. The extension tube is adapted to cooperate with the indicating and actuating members of the camera body and the lens assembly, and it can be connected in place without mechanical interference occurring between members within the extension tube and the members in the camera body and the lens assembly.
Mechanical mounting arrangements for interconnecting the above described operating members are known from U.S. Pat. Nos. 3,858,225, 3,906,534 and 3,988,748. Further, an extension tube for use between an interchangeable lens assembly and a camera body is disclosed in U.S. Pat. No. 4,003,068.
According to the above cited U.S. Patents, the interchangeable lens assembly or the extension tube is provided with a breech lock ring in threaded engagement with the lens barrel, or with the barrel of the extension tube. A bayonet mount member is fixed to the breech lock ring so that, when coupled to a corresponding bayonet mount member in the camera body, the lens assembly is attached to the camera body. During attachment of the lens assembly, its aperture indicating member and diaphragm actuating member, though otherwise movable relative to the lens barrel, are maintained stationary at certain positions relative to the lens barrel. Therefore, to establish the bayonet coupling, the operator first adjusts the relative angular position of the lens barrel to the camera body by way of an index mark, and then turns the breech lock ring. An operative relationship between the aperture indicating members, and between the diaphragm actuating members of the camera body and the lens assembly is effected at this time.
The use of the breech lock rings in the interchangeable lens assembly and the extension tube has the advantage that the barrel, which holds the aperture indicating and actuating members in stationary positions, is restrained from rotation relative to the camera body so that the accuracy of exposure information obtained from the aperture indicating members can be increased and, because the lens barrel remains stationary after attachment, optical performance is maintained at a high level. However, there is a strong likelihood of the occurrence of handling difficulties, since the operator is required to grasp the breech lock ring in order to turn it. In other words, since the breech lock ring is arranged at the rearmost position (camera end) of the barrel and, moreover, is limited in its axial length so as to avoid interference with other operating members, attachment and detachment of the barrel has been thought to be somewhat time-consuming and difficult. In order to overcome this drawback, a new lens mount device has recently been developed, as disclosed in West German OS No. 2,804,459 (claiming priority of Japanese Open Patent No. 42-11280); and West German OS No. 2,805,210 (claiming priority of Japanese Open Patent Nos. 52-12827, 52-13391, 52-13392, 52-39176, and 52-44247). The new mount device includes a guide member which supports the aperture indicating member and the diaphragm actuating member for rotation about the optical axis of the lens, a lens barrel arranged to be rotatable relative to the guide member, and a releasable locking mechanism for holding the lens barrel in a certain position relative to the guide member after the guide member engages the camera body and is held at a fixed position relative to it. This arrangement permits the operator to grasp the lens barrel at a location where the diaphragm presetting ring, indicator ring, or focusing ring is fitted when turning the barrel to attach or detach this lens mount device to or from the camera body.
The above cited U.S. Pat. No. 3,988,748 discloses a camera for use with a lens assembly or extension tube which includes aperture indicating and diaphragm actuating members. The camera body, also shown in FIG. 1 of the present drawing, is provided with an aperture indicating member A.sub.1 and a diaphragm stop down or actuating member B.sub.1 for cooperating with the corresponding indicating and actuating members in the lens assembly. Since, in operation, the members A.sub.1 and B.sub.1 move in directions indicated by arrows a and b, the aperture indicating and diaphragm actuating members A.sub.2 and B.sub.2 in the lens assembly (FIG. 2A) must assume certain positions relative to the members A.sub.1 and B.sub.1 in the camera body when the members A.sub.2 and B.sub.2 are brought into registration with the camera body with the aid of index marks, these positions being shown in solid lines in FIG. 2A. When the lens assembly is rotated about its optical axis in a direction indicated by arrow c to obtain secure coupling between the bayonet members of the lens assembly and the camera body, the aperture indicating members A.sub.1 and A.sub.2 in the camera body and the lens assembly are allowed to move to positions shown by dashed lines in FIG. 2A. The operator then turns the diaphragm presetting ring (not shown) to manually select a desired aperture value, wherein the aperture indicating member A.sub.2 in the lens assembly is moved in a reverse direction, shown by arrow a', from the position shown in dashed lines as the aperture value is varied from the minimum to the maximum value. Meanwhile, the indicating member A.sub.1 in the camera body follows the indicating member A.sub.2 in the lens assembly, and the final position of the member A.sub.1, depending upon the selected aperture value, is detected by an exposure control mechanism (not shown). When the release mechanism of the camera is actuated, the diaphragm actuating member B.sub.1 moves the actuating member B.sub.2 in a direction indicated by arrow b. This motion of the actuating member B.sub.2 causes the diaphragm presetting mechanism and the diaphragm device in the lens assembly to operate.
On the other hand, when an extension tube is inserted between a camera body including the aperture indicating member A.sub.1 and diaphragm actuating member B.sub.1, and an interchangeable lens assembly provided with the mounting device disclosed in the above-cited German and Japanese patents, the members in the camera body, extension tube and the lens assembly assume a relationship which is shown in FIG. 2B. Rotation of the diaphragm presetting ring (not shown) is transmitted through the member A.sub.2 to the member A.sub.1 in the camera body by way of an intermediate aperture indicating member A.sub.3 in the extension tube. Actuation of the camera release mechanism causes the actuating member B.sub.1 in the camera body to move in the direction of the arrow b, and this motion is transmitted by way of an intermediate diaphragm actuating member B.sub.3 in the extension tube to actuating member B.sub.2 which, in turn, transmits this motion to the diaphragm presetting mechanism and the diaphragm device in the lens assembly. In operation, the members A.sub.1, A.sub.2 and A.sub.3 move in an opposite sense to the direction of movement of the members B.sub.1, B.sub.2 and B.sub.3, as shown in FIG. 2B.
While the lens assembly including the new mount device described above is detached from the camera body, the guide member and the lens barrel are held at a certain fixed position relative to one another. When the lens assembly is attached to the camera body or to an extension tube, and the lens barrel is rotated through a certain angle to complete the bayonet coupling, an operative positional relationship is established between the indicating and actuating members in the attached pair. In order to allow the lens assembly to be attached with high accuracy and, in particular, with improved reliability, a lock mechanism is provided for preventing unintentional relative rotation between the lens barrel and the guide member after the lens barrel is rotated through the required angle to complete the bayonet coupling, as disclosed in the above cited German and Japanese patents. Further, the guide member can be locked on the camera body (or extension tube) indirectly in response to operation of the lock mechanism, that is, by way of the lens barrel. This feature, however, gives rise to a serious problem in the design of an extension tube for use with the new mount device, since the directions of movement of the aperture indicating and diaphragm actuating members (arrows a and b) and the rotation of the lens barrel (arrows c and d) are relatively complex.
FIGS. 3A and 3B are perspective views showing an arrangement by which the aperture indicating members A.sub.1, A.sub.2 and A.sub.3, and the diaphragm actuating members B.sub.1, B.sub.2 and B.sub.3 are placed in operative relationship when the lens mount device described above is coupled to an extension tube which is then attached to a camera body. It should be noted that when the lens mount device is first attached to the extension tube, the lens is handled in a manner similar to that when it is attached directly to the camera body. When the bayonet coupling of the lens mount device is engaged with the extension tube, the lock mechanism of the lock device operates, and the guide member, lens barrel, aperture indicating member A.sub.2 and actuating member B.sub.2 of the mount device are maintained in fixed positions relative to the body of the extension tube.
Attempts have been made to provide an extension tube with a mount device having operating advantages similar to those of the above described lens mount device, including a guide member which is fixed against rotation relative to the camera body and which supports aperture indicating and diaphragm actuating members for rotation about the optical axis, and a main body arranged to be rotatable relative to the fixed guide member. It has been discovered, however, that a problem may arise when such an extension tube is attached to and detached from the camera body.
Specifically, referring to FIG. 3A, after the lens assembly is attached to the extension tube and the extension tube is attached to the camera body, the aperture indicating member A.sub.2 and diaphragm actuating member B.sub.2 in the lens mount device are fixed in position relative to lens barrel F, since guide member E and the lens barrel F are locked together by lock mechanism G. Therefore, attachment of the main body of the extension tube to the camera body causes the aperture indicating member A.sub.2 and the diaphragm actuating member B.sub.2 to rotate simultaneously. In order to transmit movement between the members of the camera body and the lens mount device, it is required that aperture indicating members A.sub.1, A.sub.2 and A.sub.3, and the diaphragm actuating members B.sub.1, B.sub.2 and B.sub.3 assume the relative positions shown in FIG. 3B. However, when the actuating member B.sub.2 in the lens mount device and the actuating member B.sub.3 in the extension tube are moved from the positions of FIG. 3A to the positions of FIG. 3B, these members interfere with each other, thereby making it impossible to allow the extension tube to remain attached to the lens mount device. Conversely, when the extension tube is detached from the camera body while the lens remains attached to the extension tube, the actuating member B.sub.2 in the lens mount device interferes with the actuating member B.sub.3 in the extension tube as the indicating member A.sub.2 and the actuating member B.sub.2 in the lens mount device are rotated in the direction of arrow d, together with the main body of the extension tube.